Jets of gas released when hot and cold collide could explain what appears to be dunes.

A volcanic eruption (blue) can be seen on Jupiter's moon Io, the solar system's most volcanically active body. NASA's Galileo mission, which ended in 2003, captured this image.  DLR, JPL-CALTECH/NASA
A volcanic eruption (blue) can be seen on Jupiter’s moon Io, the solar system’s most volcanically active body. NASA’s Galileo mission, which ended in 2003, captured this image.  DLR, JPL-CALTECH/NASA

Lava creeping beneath frost on Jupiter’s moon Io may give rise to fields of towering dunes.

This discovery, published in Nature Communications on April 19, suggests that dunes may be more common in other worlds than previously thought, though the lumps may form in unusual ways.

“In some ways, these [other worlds] are starting to look more familiar,” says George McDonald, a planetary scientist at Rutgers University in Piscataway, New Jersey. “But the more you think about it, the more exotic they seem.”

Io is a world teeming with erupting volcanoes, which form when Jupiter’s and some of its other moons’ gravitational forces pull on Io and generate heat (SN: 8/6/14). Hummocky ridges were discovered on Io’s dynamic surface around 20 years ago by scientists. The features resemble dunes, but that couldn’t be because Io’s atmosphere is too thin for winds to whip up a Runescape, scientists reasoned.

However, dunelike features have been discovered on comet 67P (SN: 9/21/20) and Pluto (SN: 8/24/21), both of which lack thick atmospheres. McDonald and his colleagues returned to the subject of Io’s mysterious lumps, inspired by those alien dunescapes. All they needed was an airborne force to shape the moon’s dunes.

When molten rock flows collide with bodies of water on Earth, powerful explosions of steam occur. While there is no water on Io, sulfur dioxide frost is common. As a result, the scientists believe that when lava slowly flows into and just beneath a frost layer, jets of sulfur dioxide gas may burst from the frost. These jets could propel grains of rock and other material into the air, forming dunes.

According to the researchers, an advancing lava flow buried beneath at least 10 centimeters of frost could sublimate some of the frost into pockets of hot vapor. When enough vapor accumulates and the pressure rises to match or exceed the weight of the overlying frost, the vapor can burst out at speeds of up to 70 kilometers per hour. According to the researchers, these bursts could propel grains with diameters ranging from 20 micrometers to one centimeter.

This image was captured by NASA's now-defunct Galileo spacecraft and depicts dunelike lumps on Jupiter's third-largest moon, Io. The dark area (lower left) is a lava flow, and the bright streaks radiating outward could be evidence of material strewn by vapor jets that burst from frost heated by the lava. RUTGERS UNIV., JPL-CALTECH/NASA

This image was captured by NASA’s now-defunct Galileo spacecraft and depicts dunelike lumps on Jupiter’s third-largest moon, Io. The dark area (lower left) is a lava flow, and the bright streaks radiating outward could be evidence of material strewn by vapor jets that burst from frost heated by the lava.

RUTGERS UNIV., JPL-CALTECH/NASA
Furthermore, using the images to measure the hummocky features revealed that their dimensions match those of dunes on other planets. The team estimates that some of the Ionian dunes are over 30 meters high.
“I think a lot of [scientists] looked at those and thought, hey, these could really be dunes,” Jani Radebaugh, a planetary scientist at Brigham Young University in Provo, Utah, who was not involved in the study, says. “What’s exciting is that they’ve devised a good physical mechanism to explain how it’s possible.”
Io is commonly thought of as a volcanic world. According to McDonald, the presence of dunes suggests that there is more going on there than scientists previously thought. “It certainly adds another layer of complication.”
Source :
G. McDonald et al. Aeolian sediment transport on Io from lava-frost interactions. Nature Communications. Published online April 19, 2022. DOI: 10.1038/s41467-022-29682-x.

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